The present invention is directed to a fuel injector.
A fuel injector in which a slot-shaped outlet opening is provided at the downstream end is described in German Patent Application No. 198 47 625. The outlet opening is either formed in a perforated disk or directly on the nozzle body itself. The slot-shaped outlet openings are always introduced centrally at the longitudinal valve axis. Upstream from the valve seat is a helical groove, which imparts a circular rotary motion to the fuel flowing to the valve seat. The flat outlet orifice ensures that the fuel is spray-discharged in a fanlike manner.
The fuel injector according to the present invention has fuel sprays in fan-jet form that may easily be discharged in any desired spatial direction. The slot-shaped flow outlet provides that the jet penetrates to varying degrees across the width of the fan jet. This may produce fan-type spray fronts which penetrate the combustion chamber to varying depths during direct injection. The maximally available combustion chamber cross-section may thereby be filled with fuel spray without any significant wetting of the combustion-chamber wall. The maximum air quantity may be mixed with fuel spray without any particular wall wetting.
The width of the flow outlet may be varied since the cross-sectional area of the flow outlet changes as a function of the hydraulic pressure acting on the slot-forming element and the plastic deformation of the slot-forming element in the area of the free circumferential section that it entails. The flow-rate of the valve (dynamic flow quantity) may be selectively changed and set. The dynamic range of a fuel injector is thereby able to be enlarged toward small spray-discharge quantities. Even smaller, precisely metered spray-discharge quantities may be possible in idle operation at lowered system pressure.
The pressure-controlled variation of the width of the flow outlet may also make it possible to vary the width of the fan jet, that is, the propagation angle of the jet fan. Since the slot-cross section is lenticular, the mass-flow portion at the two pointed slot ends is less than the mass flow portion in the central region of the flow outlet. If the slot width is reduced, the mass portion emerging at the two slot ends is correspondingly lower yet, so that the slot length effectively traversed by the flow is reduced in response to a reduction in the slot width. Consequently, the propagation angle of the jet fan, given a pressure drop, is likewise reduced. At low engine loads, this provides for an appropriately reduced propagation of the spray cloud in the combustion chamber, which may meet power efficiency demands.
The static flow quantity may be adjusted via the width of the flow outlet. At the end of the valve manufacturing process, the slot width is adjusted by mechanical bending of the slot-forming element.
The danger of carbon deposits forming in the flow outlet may be reduced by the pressure pulsations during valve operation, since the flow outlet xe2x80x9cbreathesxe2x80x9d, due to the constant width variation. This xe2x80x9cbreathingxe2x80x9d mechanically removes deposits in the area of the flow outlet.